This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-042730, filed Feb. 2, 1999, the entire contents of which are incorporated herein by reference.
This invention relates to an ion implantation method and ion implantation equipment.
An ion implantation method is known as a method for doping impurity atoms into a semiconductor substrate. Since the concentration and depth of impurity atoms to be doped into a target region can be controlled with high precision, the ion implantation method becomes an important technique for manufacturing semiconductor devices in the present day.
As one of the conventional ion implantation equipments, there is provided an ion implantation equipment which has an extraction electrode 2 for introducing plural types of ions generated in an ion source chamber into a mass spectrograph while accelerating them and a post accelerator 5 for accelerating ions having a desired mass subjected to mass spectrometry in the mass spectrograph and taken out through a slit to final acceleration.
The acceleration voltage is controlled by acceleration by the extraction electrode and acceleration by the post accelerator. For example, if ion is implanted into a sample by use of the acceleration voltage of 120 keV, the acceleration voltage control operation is effected according to a combination of xe2x80x9cmaximum acceleration by the extraction electrodexe2x80x9d+xe2x80x9cacceleration by the post acceleratorxe2x80x9d.
The acceleration by the post accelerator only assists in an insufficient portion which cannot be attained by the maximum acceleration by the extraction electrode and the acceleration by the post accelerator is lower than the maximum acceleration by the extraction electrode. The reason why the maximum acceleration by the extraction electrode is made higher is to enhance the throughput in the implantation step by efficiently transporting an ion beam and stably acquire a constant amount of ion beam current.
Further, if ion is applied to a sample by use of the acceleration voltage of 5 keV, only the acceleration by the extraction electrode is used or an xe2x80x9cacceleration by the extraction electrodexc3x97deceleration by the port acceleratorxe2x80x9d method, that is, an accelerationxc3x97deceleration (accelxc3x97decel) method, is used.
An object of this invention is to provide an ion implantation method capable of uniformly implanting ions into a sample by use of an ion implantation equipment having a first electrode (extraction electrode) and a second electrode (post accelerator).
In order to attain the above object, in an ion implantation method using an ion implantation equipment having a container for generating plural types of ions therein, a first electrode for extracting the plural types of ions from the container, a selector section for selecting at least one desired type of ion from the plural types of ions, and a second electrode for accelerating the desired type of ion, an ion implantation method according to this invention has a feature that an applied volt. of the second electrode is set higher than an applied volt. of the first electrode.
In this invention, it is preferable to attain the relation of xcfx81xe2x89xa7Dmax/2 if the maximum current density in the ion beam formed of ions accelerated by the second electrode is Dmax, the amount of current of the ion beam is I, the width of the ion beam is W, and the average current density expressed by I/W2 is xcfx81. In this case, the width of the ion beam is the width on the surface of the sample into which ion is implanted.
According to the study of the inventor of this application and the like, in an ion implantation method using an ion implantation equipment having a container for generating plural types of ions therein, a first electrode for extracting the plural types of ions from the container, a selector section for selecting at least one desired type of ion from the plural types of ions, and a second electrode for accelerating the desired type of ion, it is proved that ion can be uniformly implanted into the sample if an applied volt. of the second electrode is set higher than an applied volt. of the first electrode. Particularly, it is proved that the above effect can be further enhanced when the relation of xcfx81xe2x89xa7Dmax/2 is set up if the maximum current density in the ion beam formed of ions accelerated by the second electrode is Dmax, the amount of current of the ion beam is I, the width of the ion beam is W, and the average current density expressed by I/W2 is xcfx81. Therefore, according to this invention, it is possible to uniformly implant ion into the sample.
Another object of this invention is to provide an ion implantation equipment capable of suppressing a lowering in the ion implantation amount and the concentration of active ion.
In order to attain the above object, an ion implantation equipment according to this invention comprises an ion implantation equipment main body for implanting desired type of ion into a sample; an oxide film removing device connected to the ion implantation equipment main body, for removing an oxide film formed on the surface of the sample; and an oxide film removing device for removing an oxide film formed on the surface of the sample prior to implantation of the accelerated ion into the sample.
In this invention, as an example of the concrete construction of the oxide film removing device, a cleaning chamber for removing the oxide film formed on the surface of the sample before implanting the accelerated ion into the sample, a drying chamber for drying the sample cleaned in the cleaning chamber, a transferring section for transferring the sample into the sample chamber, cleaning chamber and drying chamber, and a pressure control section for controlling the pressures in the sample chamber, cleaning chamber and drying chamber are provided.
The pressures in the sample chamber, cleaning chamber and drying chamber are controlled to reduced pressure (lower than one atmospheric pressure), preferably 5 Torr or less, and more preferably, 0.1 Torr or less by the pressure control section.
The ion implantation equipment according to this invention may include a first electrode (extraction electrode) and second electrode (post accelerator) or it may include only a second electrode (post accelerator).
The oxide film formed on the surface of the sample may be an important factor for causing the ion implantation amount of the concentration of active ion to be made lower than expected if ion is implanted into the sample surface, particularly, if ion is implanted into a shallow region as viewed from the surface of the substrate, more specifically, if ion is implanted into a shallow region of 50 nm or less from the surface of the sample.
Therefore, according to this invention, since it becomes possible to set up a state in which no oxide film is re-formed on the surface of the sample in a period from removal of the oxide film to the end of the ion implantation by connecting the oxide film removing device for removing the oxide film formed on the surface of the sample to the sample chamber, an ion implantation equipment capable of suppressing a lowering in the ion implantation amount and the concentration of active ion can be realized.